Some cathode-ray tubes include a microchannel plate positioned immediately adjacent and parallel to a display screen to enhance the brightness of an image formed thereon. For example, U.S. Pat. No. 4,752,714 of Sonneborn et al. for "Decelerating and Scan Expansion Lens System for Electron Discharge Tube Incorporating a Microchannel Plate," describes such a tube in which a beam of electrons emitted from a point-type electron source propagates generally along a beam axis. The beam is scanned across an input side of the microchannel plate by means of a pair of deflection structures in cooperation with an electrostatic scan expansion lens system. The scan expansion lens system is positioned between the deflection structures and the microchannel plate to magnify the deflection angle provided by the deflection structures. Accordingly, the scan expansion lens system receives electrons emitted from the point-type electron source and directs them toward the microchannel plate.
In response to the electron beams scanned across its input side, the microchannel plate provides at an output side an increased number of electrons that propagate toward the display screen. Each location on the microchannel plate is aligned in opposed relation to a corresponding location on the display screen. An enlarged cross-sectional view of such an arrangement is shown by Sonneborn et al. in FIG. 1 of "Design of a Microchannel Plate CRT for a General-Purpose Oscilloscope," pp. 240-243, SID 1986 Digest. The microchannel plate in such a cathode-ray tube is, therefore, of a diagonal size substantially the same as that of the display screen.
Cathode-ray tubes of this type suffer from at least two disadvantages. Microchannel plates are relatively expensive and have a cost that is directly proportional to their diagonal size. In addition, microchannel plates with a diagonal size greater than about 4 cm. are difficult to manufacture. As a result, the diagonal size of the display screen in such a tube is typically less than about 2.5 cm. because of the expense of and difficulty in manufacturing microchannel plates of a larger size.